This invention relates to angular position sensors, and in particular, a magnetic non-contacting angular position sensor whose output signal is linearly related to angular position over a range of xc2x190xc2x0.
It is known in the art relating to angular position sensors that a magnetic non-contacting angular position sensor may provide a linear output over a limited measurement range of xc2x155 to 60xc2x0. Applications for most commercially availably prior art sensors are limited by the structure of the sensor, which requires the rotating member, i.e. the permanent magnet, to rotate at the center of the sensor, with certain stationary components including a Hall probe being located outside the magnet. Prior art sensors which do teach a rotating magnet rotating about interiorly located stationary components, however, require the rotating magnet member to be cylindrical or tubular in shape with a cylindrical gap separating the rotating member and the stationary components. The requirement of a cylindrical gap between the stationary components and the rotating member limits the size, shape and arrangement of both the permanent magnet and the stationary components, which necessarily increases the cost of manufacture.
The present invention provides a low cost, versatile non-contacting angular position sensor that provides a linear output over a greater range than that of the prior art sensors. According to the present invention, a permanent rotating magnet may be coupled to a rotating shaft at the center of the sensor with the stationary components (a Hall sensor disposed between a pair of soft steel flux concentrators) located coaxially outside the magnet, or it may be coupled to a rotating outer hub with the stationary components fixed at the center of the sensor. There is no shape requirement for the gap between the rotating magnet and the stationary components. In fact, analysis has shown that varying the size and shape of the gap has little effect on the range of linear output. If the gap is too wide, however, signal strength is compromised. Accordingly, an ideal range for the gap is 0.5-2 mm. Both arrangements provide a linear output over a range of xc2x190xc2x0.
The present invention advantageously reduces the cost of materials while increasing the range of linear output, by providing a permanent, radially magnetized arc segment magnet whose enclosed angle is only 20-40% greater than the arc of the concentrator, the size of which directly corresponds to the range of desired measurement. Thus, if the desired range of measurement is xc2x190xc2x0 (180xc2x0), then the sensor will provide linear output where the flux concentrators form an arc of approximately 180xc2x0, and the arc segment magnet is in the range of approximately 220-250xc2x0. Accordingly, if the desired range of measurement is xc2x160xc2x0, the flux concentrators should form an arc of 120xc2x0, and the arc angle of the segment magnet should be in the range of approximately 145-165xc2x0.
The present invention also includes a programmable Hall sensor, situated between a pair of soft magnetic flux concentrators. Because the size of the rotating magnet is reduced, the size of the flux concentrators is likewise reduced. Optimum results are achieved where the flux concentrators form an arc of 180xc2x0, less than the enclosed angle of the arc segment magnet.
Because both the Hall sensor and the flux concentrators remain stationary, any field generated by the rotating magnet moves from one end of one flux concentrator, to the end of the second flux concentrator, straight across the Hall sensor. The Hall sensor produces a direct 0 to 5 V d.c. voltage that varies linearly with the position of the magnet as it rotates through xc2x190xc2x0. When the magnetic flux is perpendicular to the Hall sensor, the sensor output is at its maximum, even though flux strength remains constant. Depending on the location of the magnetic poles and the direction of the chip within the Hall sensor, the angular position sensor may be calibrated so that when the magnet is rotated in one direction, clockwise, for example, the voltage will read from 2.5 to +5 volts and when the rotation of the magnet is reversed, the voltage will read from 0 to 2.5 volts where 2.5 V represents 0 flux.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.